Yes, I pointed this out before on c.l.lisp but there has to be some upside to senility and freely repeating myself is it: an OpenLaszlo introductory video.
Pretty far into the video, after some horrifyingly dirty language like "JDOM" which was all the more horrifying for the speaker clearly believing he was talking plainly (driving home my dinosaurosity and at the same time making me feel a whole lot better about it) we learn that OpenLaszlo includes as one bell amidst all the whistles...wait for it... dataflow! ta-dum!!! Pretty damn transparently, to boot.
Meanwhile over in the comp.lang.lisp archives you'll find the author of the latest Common Lisp tome saying he cannot see the point of my equivalent Cells library and news of my invitation to ECLM 2008 where I have been invited to unravel this profound mystery live and in color as if that will make any difference.
Meanwhile back in the above video we discover the speaker presuming the advantages are obvious to his audience and offering no further explanation beyond pointing it out.
Tilton's Law: Solve the Right Problem. Maybe I do not need to explain dataflow better, maybe I need a new audience.
ps. In the yobbos's defense, I just checked the Laszlo white paper on their product and they do not even mention dataflow explicitly. Just a couple of mentions of layout being "declarative". :)